The present invention relates to a tracking control circuit and method which are suitable for use in a rotary head type digital tape recorder by way of example.
A rotary head type digital audio tape recorder (hereinafter referred to as DAT) has conventionally been used as a magnetic recording/reproducing apparatus capable of recording an audio signal with high density.
The DAT is designed such that input audio data are recorded on a magnetic tape wound around a rotary drum at a predetermined winding angle by using a rotary head arranged on the rotary drum, or the recorded audio data recorded on the magnetic tape are reproduced (played back) by using the rotary head.
In this connection, to properly reproduce the recorded audio data recorded on the magnetic tape, it is required that the rotary head precisely tracks over recording tracks of the magnetic tape.
To this end, a tracking control method with the so-called ATF (automatic track following) technique has been employed in the DAT.
More specifically, as shown in FIG. 1, a magnetic tape 1 on which audio data are recorded in accordance with the DAT format has formed thereon recording tracks TA, TB successively and alternately recorded by a rotary head 2, having positive and negative azimuth angles, as indicated by the diagonal line patterns, in an oblique direction AW2 relative to the running direction AW1 of the magnetic tape 1.
At predetermined positions in the lower and upper ends of each of the recording tracks TA, TB, there are respectively formed first and second ATF recording regions ATF1 and ATF2 in each of which an ATF synchronizing signal and an ATF pilot signal are recorded.
Between the first and second ATF recording regions ATF1 and ATF2, there is formed a data recording region DATA in which digital audio data are recorded with each pair of first and second recording tracks TA and TB being as one recording unit (i.e. a so-called interleave unit).
In the reproducing operation with the above arrangement, when the ATF synchronizing signals in the first and second ATF recording regions ATF1 and ATF2 of one recording track TA, for example, are detected based on a reproduced RF (radio frequency) signal obtained from the rotary head 2, the ATF pilot signals recorded on the preceding and succeeding recording tracks TB adjacent to the recording track TA are read out dependent on the detection timing of the ATF synchronizing signals in a time-sharing manner, whereby first and second ATF error signals corresponding to offtrack amounts at the lower and upper ends of the magnetic tape 1 are obtained dependent on a level difference between the ATF pilot signals read-out.
Thus, by controllably driving the running speed of the magnetic tape 1 in accordance with the first and second ATF error signals, the rotary head 2 can precisely track over the predetermined recording track TA of the magnetic tape 1.
In practice, as shown in FIG. 2(A), a DAT's rotary heads 2A, 2B having positive and negative azimuth angles, respectively are arranged on a rotary drum 3 with a diameter of 90 mm to be spaced from each other by an angular spacing of 180 degrees, while the magnetic tape 1 is wound around the rotary drum 9 over an angular span of 90 degrees.
This DAT is controlled such that while the rotary drum 3 rotates once, the first and second rotary heads 2A and 2B scan once over the first and second recording tracks TA and TB on the magnetic tape 1, respectively, and send out a reproduced RF signal RF.sub.TA resulting from the first rotary head 2A reproducing the first recording track TA during the period while the rotary drum 3 is rotating from 0 degrees to 90 degrees and a reproduced RF signal RF.sub.TB resulting from the second rotary head 2B reproducing the second recording track TB during the period while the rotary drum 3 is rotating from 180 degrees to 270 degrees, as shown in FIG. 3(A), taking as a reference the timing at which the first rotary head 2A starts scanning the first recording track TA, for example.
During the periods while the rotary drum 3 is rotating from 90 degrees to 180 degrees and from 270 degrees to 360 degrees, neither the first nor the second rotary heads 2A, 2B are brought into contact with the magnetic tape 1.
The DAT detects the ATF synchronizing signals from the reproduced RF signals RF.sub.TA and RF.sub.TB at timing points T.sub.ATF1, T.sub.ATF2 spaced at substantially equal intervals dependent on the recording format, as shown in FIG. 3(B), and it also samples an ATF error signal given by the difference between the ATF pilot signals obtained in accordance with the detected ATF synchronizing signals. The DAT then holds the sampling value until the timing of the subsequent ATF synchronizing signal, and controllably drives the feed speed of the magnetic tape 1.
In some types of conventional DATs, a rotary drum 4 with a diameter of 15 mm is used in place of the rotary drum 3 with a diameter of 30 mm to reduce the size of the mechanical mechanism section.
In this type DAT, as shown in FIG. 2(B), the rotary heads 2A and 2B are arranged on the rotary drum 4 with a diameter of 15 mm to be spaced from each other by an angular spacing of 180 degrees, while the magnetic tape 1 is wound around the rotary drum 4 over an angular span of 180 degrees.
This DAT is controlled such that while the rotary drum 4 rotates once, the first and second rotary heads 2A and 2B scan once over the first and second recording tracks TA and TB on the magnetic tape 1, respectively, and send out a reproduced RF signal RF.sub.TA1 resulting from the first rotary head 2A reproducing the first recording track TA during the period while the rotary drum 4 is rotating from 0 degrees to 180 degrees and a reproduced RF signal RF.sub.TB1 resulting from the second rotary head 2B reproducing the second recording track TB during the period while the rotary drum 4 is rotating from 180 degrees to 380 degrees, as shown in FIG. 3(C), taking as a reference the timing at which the first rotary head 2A starts scanning the first recording track TA, for example.
The DAT detects the ATF synchronizing signals from the reproduced RF signals RF.sub.TA1 and RF.sub.TB1 at the timing points T.sub.ATF10, T.sub.ATF20, dependent on the recording format, as shown in FIG. 3(D), and it also samples an ATF error signal given by a difference between the ATF pilot signals obtained in accordance with the detected ATF synchronizing signals. The DAT then holds the sampling value until the timing of the subsequent ATF synchronizing signal, and controllably drives the feed speed of the magnetic tape 1.
In this case, however, since the timing points T.sub.ATF10, T.sub.ATF20 of the ATF synchronizing signals are not obtained with equal intervals, tracking control can be made using the lower end of the recording tracks TA, TB, but not on the upper end thereof, possibly causing an off-track condition.
This problem is attributable to the fact that the ATF error signal is sampled at timing points of unequal intervals, and the sampling value is held for the same time constant until the timing of the subsequent ATF synchronizing signal.
It is therefore conceivable that the above problem is solved by changing the time constant for sample holding dependent on the interval of the ATF synchronizing signals detected. But this is unsatisfactory for practical use due to another problem of complicating the circuit and increasing its size.